An example of a substrate processing apparatus includes a semiconductor manufacturing device, and a longitudinal apparatus has been known as an example of a semiconductor manufacturing device. In the example of the substrate processing apparatus, a boat is included as a substrate retaining member configured to retain substrates (wafers) in a reaction tube in a multi-stage manner, and the substrates are processed in a process chamber in the reaction tube in a state in which the plurality of substrates are retained on the boat.
Japanese Unexamined Patent Application Publication No. 2011-52319 discloses that a plurality of wafers 200 which are to be processed in a batch are inserted into a reaction tube 203 while the plurality of wafers 200 are stacked on a boat 217 in a multi-stage manner, at least two types of sources are simultaneously supplied into the reaction tube 203, and a film is formed on the wafers 200 placed in the reaction tube 203.
However, as illustrated in FIG. 9A, since an upper tubular portion of a conventional reaction tube 203 is dome-shaped, a large space is formed between an upper internal surface of the reaction tube 203 and a ceiling plate 211 formed on the top of the boat 217. Thus, in an upper region in the reaction tube 203 (hereinafter referred to as a ‘top region’), a gas is supplied into a process chamber 201 via gas supply holes formed in a nozzle 710. Then, the gas flows upward in the reaction tube 203 and is then exhausted via an exhaust pipe in a low portion of the reaction tube 203. A part of the gas flowing upward in the reaction tube 203 is stagnant in the top region, thereby causing a non-uniform distribution of the gas in the top region. Also, as illustrated in FIG. 9B, when the reaction tube 203 having plasma generation structures 429 is used, a buffer chamber 423 is installed in the reaction tube 203 and a gas is thus likely to stagnate in an upper space in a buffer chamber wall 424 forming the buffer chamber 423, thereby causing a non-uniform distribution of the gas in the top region.